The invention relates to a control system and method for maintaining the desired compressed fluid discharge temperature in a fluid compressor aftercooler, and more particularly the invention relates to a control system for maintaining a constant aftercooler compressed fluid discharge temperature by changing the position and orientation of at least one fluid flow regulating member based on the measured ambient temperature.
Conventional fluid compressors include a compression module which is comprised of an airend driven by a prime mover. Such airends are well known to those skilled in the art and usually include interengaging male and female rotors that rotate about parallel axes. A fluid, such as air, is supplied to the airend through the airend inlet, is compressed by the rotors, and is discharged out the airend discharge port or outlet. The compressed discharged fluid is hot and must be cooled before it may be supplied to an object of interest such as a pneumatic tool. In conventional fluid compressors the hot compressed fluid is flowed through an aftercooler that is flow connected to the airend discharge port. The aftercooler serves to cool the hot compressed fluid so that the compressed fluid supplied to the object of interest is at a desirable temperature.
A prior art aftercooler system is shown in FIG. 1 and is identified generally at 10. The aftercooler unit 11, has an inlet 12 through which hot, compressed fluid is supplied to the aftercooler from the airend (not shown) and a discharge port 13 through which the cooled, compressed fluid is flowed out of the aftercooler to an object of interest. Ambient cooling air is drawn across the aftercooler in the direction of arrows 18 by fan 17. The speed of the fan is controlled by electric fan motor 16. Temperature sensor 14 senses the temperature of the fluid discharged from aftercooler 11. The sensor is electrically connected in signal transmitting relation with microprocessor based controller 15. The system controller uses a Proportional-Integral-Derivative (PID) temperature control method well known to those skilled in the relevant art to determine the fan speed required to draw the sufficient volume of fluid through the aftercooler and cool the hot compressed fluid to the predetermined desired temperature. The controller 15 is electrically connected in signal transmitting relation to the fan motor 16.
In operation, the temperature sensor 14 senses the temperature of the fluid discharged from the aftercooler 11, and sends a signal representing the sensed discharge fluid temperature to the controller 15. If the sensed discharge fluid temperature is outside the desired range, the controller initiates the PID control logic and thereby determines the fan speed required to obtain the desired aftercooler discharge temperature. The controller sends a signal to the fan motor 16 altering the fan speed as required.
Although the prior art aftercooler control systems are generally effective at achieving the desired aftercooler discharge temperature there are a number of shortcomings associated with such prior art systems. First, because the PID control method relies on a derived algorithm to obtain the best performance, the derived must fit the compressed air system being monitored. Frequently, the algorithm proves difficult to derive accurately and does not include the correct constant values. If the algorithm is not tuned or derived to the required accuracy, the PID system will produce less than optimum results. Second, prior art aftercooler temperature control systems use only aftercooler outlet temperature to determine if the fan speed needs to be altered and only using the discharge temperature as the measurement can produce instabilities in the PID control loop performance. Finally, prior art systems frequently are analog systems that use electric or pneumatic controllers and such pneumatic based controllers are prone to freezing in cold weather, and electric systems can experience "hunting" or oscillating problems which produce unstable compressor operation.
The foregoing illustrates limitations known to exist in present aftercooler temperature control systems and methods. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.